The present invention relates to an electrochemical device, for sensing fluid components and particularly gases, which utilizes a solid ionic electrolyte. Prior art fluid component sensors, e.g., polarographic oxygen sensors, typically use an electrolytic cell having two electrodes separated by a liquid electrolyte. One of the electrodes and/or the electrolyte is exposed through a permeable membrane to the oxygen to be assayed. The disadvantages of these cells are their bulk and inability to function at temperatures which would ordinarily evaporate or freeze the solution.
More recently, in U.S. Pat. No. 3,764,269 there is suggested an improved sensor for fluid components. The disclosed sensor comprises a thin membrane through which the component passes to react with a composition to liberate elemental chlorine, bromine, fluorine or iodine. The chlorine, bromine, fluorine or iodine passes through a porous graphite layer and activates the positive electrode of a solid ionic electrolyte battery of the type: halogen/solid ionic electrolyte/metal electrode, whereby a current flow is generated through a measuring device, the current being proportional to the concentration of the fluid component.
The suggested device overcame many of the problems of prior art sensors in that it was compact and could be operated over a wide range of temperatures. Nonetheless, such a device is not without need of improvement. More particularly, the current generated by such a device is of very low magnitude and requires a highly sensitive current measuring device or the use of some external means for amplifying the magnitude of current flow such that it is more readily readable with commercially available instrumentation. In addition, the response time of the suggested device is substantially slower than is desirable. Another disadvantage of such a device is that it has been found that it is relatively unstable with respect to time and to obtain accurate measurements it must be calibrated at least daily when in constant use.